Sign up for our NewsAlert service and have the latest news in astronomy and space e-mailed direct to your desktop.
Enter your e-mail address:Privacy note: your e-mail address will not be used for any other purpose.

Solar physicists from Lockheed Martin and the Solar Physics and upper-Atmosphere Research Group at the Department of Applied Mathematics of the University of Sheffield, UK have used computer modeling and some of the highest resolution images ever taken of the solar atmosphere to explain the cause of supersonic jets that continuously shoot through the low atmosphere of the Sun.

This image, taken at the Swedish 1-meter Solar Telescope on the island of La Palma, Spain, shows Active Region 10380 on the Sun. Credit: Lockheed
Martin

Their results, which appear as the cover story in the July 29 issue of
the journal Nature, directly address the origin of these jets, called
spicules. The origin of spicules has been a mystery since their
discovery in 1877. These findings may well lead to a better
understanding of how matter is propelled upward into the solar corona
to form the solar wind, a stream of particles continuously emitted by
the Sun that sweeps past Earth's orbit. Disturbances in the solar wind
can influence the upper atmosphere and space environment around the
Earth and damage satellites in orbit.

"The combination of computer modeling, new high resolution images
taken with the Swedish 1-meter Solar Telescope (SST) on the island of
La Palma, Spain and data taken simultaneously with two satellites in
space, was crucial to figure out how spicules are formed," said Dr.
Bart De Pontieu, one of the main investigators on the study, and solar
physicist at the Lockheed Martin Solar and Astrophysics Lab (LMSAL) at
the company's Advanced Technology Center in Palo Alto, Calif. "We used
a computer model to provide the missing link between observations of
the surface of the Sun, taken with the MDI instrument onboard
ESA/NASA's Solar and Heliospheric Observatory (SOHO) satellite, and
observations of the jets in the low solar atmosphere taken with the
SST and NASA's Transition Region and Coronal Explorer (TRACE)
satellite."

Spicules are jets of gas or plasma propelled upwards from the surface
of the Sun. They shoot into its atmosphere or corona at supersonic
speeds of about 50,000 miles per hour, and reach heights of 3,000 miles
above the solar surface in less than five minutes. Although there are
over 100,000 spicules at any time in the Sun's low atmosphere, or
chromosphere, they remain largely unexplained, in part because
observations are difficult for objects with so brief a lifetime (about
five minutes) and relatively small size (300 miles diameter).

By simultaneously taking a series of high resolution images with the
Swedish Solar Telescope, showing details down to 80 miles, and with the
TRACE satellite, we discovered that these jets often occur
periodically, usually every five minutes or so, at the same location,"
said Professor Robertus Erdelyi von Fay-Siebenbuergen, the other main
investigator on the study, and professor in applied mathematics at the
Solar Physics and upper-Atmosphere Research Group of the University of
Sheffield, UK. "We developed a computer model of the Sun's atmosphere
to show that the periodicity of the spicules is caused by sound waves
at the solar surface that have the same five minute period."

The sound waves at the solar surface are usually damped before they can
reach the Sun's atmosphere. However, De Pontieu, Erdelyi and Stewart
James, a newly graduated Ph.D. under the supervision of Professor
Erdelyi at the University of Sheffield, found that under certain
conditions, the sound waves can penetrate through the damping zone and
leak into the solar atmosphere. Their computer model shows that after
the sound waves leak into the atmosphere, they develop into shock waves
that propel matter upwards, forming a spicule.

De Pontieu and his colleagues measured actual waves and oscillations at
the surface of the Sun, using these measurements to drive their
computer model of the solar atmosphere, which then predicted when jets
of gas should shoot up. They were pleasantly surprised to see that the
model predicts very accurately when jets should be observed on the Sun
with the SST and TRACE.

"Spicules carry more than 100 times the mass into the Sun's atmosphere
required to feed the solar wind," said De Pontieu, "which means that
they are of huge importance for the balance of how much mass goes into
and out of the corona." With the origins of spicules revealed, it will
be possible to study whether the mass that spicules carry into the
solar corona contributes to the solar wind. Future studies will also
focus on the role the shock waves may play in the higher solar
atmosphere or corona.

The results of this study are in a paper published in the journal
Nature. The authors are Dr. Bart De Pontieu of Lockheed Martin Solar
and Astrophysics Lab, and Professor Robertus Erdelyi von
Fay-Siebenbuergen and Dr. Stewart James of The Solar Physics and
upper-Atmosphere Research Group at the Department of Applied
Mathematics, University of Sheffield, UK. Funding for the studies came
from NASA, the Particle Physics and Astronomy Research Council of the
UK and the Hungarian National Science Foundation.

The Lockheed Martin Solar and Astrophysics Lab is part of Lockheed
Martin's Advanced Technology Center -- the research and development
organization of Lockheed Martin Space Systems Company. Headquartered
in Bethesda, Md., Lockheed Martin employs about 130,000 people
worldwide and is principally engaged in the research, design,
development, manufacture and integration of advanced technology
systems, products and services. The corporation reported 2003 sales
of $31.8 billion.